Carbon dioxide absorbent and method of using the same

ABSTRACT

In accordance with one aspect, the present invention provides a composition which contains the amino-siloxane structures I, or III, as described herein. The composition is useful for the capture of carbon dioxide from process streams. In addition, the present invention provides methods of preparing the amino-siloxane composition. Another aspect of the present invention provides methods for reducing the amount of carbon dioxide in a process stream employing the amino-siloxane compositions of the invention, as species which react with carbon dioxide to form an adduct with carbon dioxide.

This application is a Divisional application of Ser. No. 12/817,276,filed on Jun. 17, 2010, the contents of which are incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with Government support under grant numberDE-NT0005310 awarded by the Department of Energy-NETL. The Governmenthas certain rights in the invention.

BACKGROUND

The invention relates to amino-siloxane compositions and their use ascarbon dioxide absorbent materials.

Pulverized coal power plants currently produce over half the electricityused in the United States. In 2007, these plants emitted over 1900million metric tons of carbon dioxide (CO₂), and as such, accounted for83% of the total CO₂ emissions from electric power generating plants and33% of the total U.S. CO₂ emissions. Eliminating, or even reducing theseemissions, will be essential in any plan to reduce greenhouse gasemissions.

Separating CO₂ from gas streams has been commercialized for decades infood production, natural gas sweetening, and other processes. Aqueousmonoethanolamine (MEA) based solvent capture is currently considered tobe the best commercially available technology to separate CO₂ fromexhaust gases, and is the benchmark against which future developments inthis area will be evaluated. Unfortunately, amine-based systems were notdesigned for processing the large volumes of flue gas produced by apulverized coal power plant. Scaling the amine-based CO₂ capture systemto the size required for such plants is estimated to result in an 83%increase in the overall cost of electricity from such a plant. Applyingthis technology to all existing pulverized coal power plants in the U.S.could cost $125 billion per year, making MEA-based CO₂ capture anundesirable choice for large-scale commercialization.

There are many properties that desirably would be exhibited, orenhanced, in any CO₂ capture technology contemplated to be a feasiblealternative to the currently utilized MEA-based systems. For example,any such technology would desirably exhibit a high net CO₂ capacity andelimination of the carrier solvent (for example water), and couldprovide lower capital and operating costs (less material volume requiredto heat and cool, therefore less energy required). A lower heat ofreaction would mean that less energy would be required to release theCO₂ from the material. Desirably, the technology would not require apre-capture gas compression, so that a high net CO₂ capacity could beachieved at low CO₂ partial pressures, lowering the energy required forcapture. Technologies utilizing materials with lower viscosities wouldprovide improved mass transfer, reducing the size of equipment needed,as well as a reduction in the cost of energy to run it. Low volatilityand high thermal, chemical and hydrolytic stability of the material(s)employed could reduce the amount of material needing to be replenished.Of course, any such technology would also desirably have low materialcosts, so that material make-up costs for the system would be minimized.The operability of CO₂ release at high pressures could reduce the energyrequired for CO₂ compression prior to sequestration. Finally, suchtechnologies would also desirably exhibit reduced corrosivity to helpreduce capital and maintenance costs, and further would not requiresignificant cooling to achieve the desired net CO₂ loading, reducingoperating costs.

Unfortunately, many of the above delineated desired properties interactand/or depend on one another, so that they cannot be variedindependently. Trade-offs are therefore required. For example, in orderto have low volatility, the materials used in any such technologytypically must have a relatively high molecular weight. However, inorder to achieve low viscosity, the materials must typically have arelatively low molecular weight. Moreover, in order to achieve high CO₂capacity at low pressures, the overall heat of reaction of the absorbentmaterial with carbon dioxide (to form an adduct comprising structuralunits derived from the absorbent material and CO₂) should be relativelyhigh. However, the ease of regeneration of the absorbent material andcarbon dioxide from the adduct would benefit from a relatively low heatof reaction.

Therefore there is a need for a CO₂ capture technology that optimizes asmany of the above desired properties as possible, without causingsubstantial detriment to other desired properties. At a minimum, inorder to be commercially viable, such technology would desirably beutilized at a relatively low cost, and would also utilize materials(s)having low volatility, high thermal stability, and a high net capacityfor CO₂.

BRIEF DESCRIPTION

In accordance with one aspect, the present invention provides anamino-siloxane composition comprising structure I

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; R³ isindependently at each occurrence R¹ or R⁴, wherein R⁴ comprisesstructure II

and wherein R² is independently at each occurrence hydrogen or a C₁-C₁₀aliphatic radical; X is independently at each occurrence a NH₂ group ora cyano group; m is independently at each occurrence an integer from1-5; n is independently at each occurrence an integer from 0-5; and m isindependently at each occurrence an integer from 1-5; p is an integerfrom 0-100 and q is an integer from 0-500, with the proviso that atleast one of R³ is R⁴.

In another aspect, the present invention provides an amino-siloxanecomposition comprising structure III

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; X isindependently at each occurrence a NH₂ group or a cyano group; n isindependently at each occurrence an integer from 0-5 and m isindependently at each occurrence an integer from 1-5.

In another aspect, the present invention provides a method of reducingthe amount of carbon dioxide in a process stream, comprising the step ofcontacting the stream with a carbon dioxide absorbent comprising atleast one amino-siloxane compound selected from the group consisting ofamino-siloxanes having structure I and amino-siloxanes having structureIII,

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; R³ isindependently at each occurrence R¹ or R⁴, wherein R⁴ comprisesstructure II

and wherein R² is independently at each occurrence hydrogen or a C₁-C₁₀aliphatic radical; X is independently at each occurrence a NH₂ group ora cyano group; m is independently at each occurrence an integer from1-5; n is independently at each occurrence an integer from 0-5; p is aninteger from 0-100 and q is an integer from 0-500; with the proviso thatat least one of R³ is R⁴.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings. Unless defined otherwise, technical and scientific terms usedherein have the same meaning as is commonly understood by one of skillin the art to which this invention belongs.

The terms “first”, “second”, and the like, as used herein do not denoteany order, quantity, or importance, but rather are used to distinguishone element from another. Also, the terms the terms “front”, “back”,“bottom”, and/or “top”, unless otherwise noted, are merely used forconvenience of description, and are not limited to any one position orspatial orientation. If ranges are disclosed, the endpoints of allranges directed to the same component or property are inclusive andindependently combinable (e.g., ranges of “up to about 25 wt. %, or,more specifically, about 5 wt. % to about 20 wt. %,” is inclusive of theendpoints and all intermediate values of the ranges of “about 5 wt. % toabout 25 wt. %,” etc.). The modifier “about” used in connection with aquantity is inclusive of the stated value and has the meaning dictatedby the context (e.g., includes the degree of error associated withmeasurement of the particular quantity). Similarly, “free” may be usedin combination with a term, and may include an insubstantial number, ortrace amounts, while still being considered free of the modified term.Here and throughout the specification and claims, range limitations maybe combined and/or interchanged. Such ranges are identified and includeall the sub-ranges contained therein, unless context or languageindicates otherwise.

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein, the term “solvent” can refer to a single solvent or amixture of solvents.

As used herein the term “aliphatic radical” refers to an organic radicalhaving a valence of at least 1, including a linear or branched array ofatoms, which is not cyclic. Aliphatic radicals are defined to compriseat least one carbon atom. The array of atoms comprising the aliphaticradical may include heteroatoms such as nitrogen, sulfur, silicon,selenium and oxygen, or may be composed exclusively of carbon andhydrogen. For convenience, the term “aliphatic radical” is definedherein to encompass, as part of the “linear or branched array of atomswhich is not cyclic”, a wide range of functional groups such as alkylgroups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugateddienyl groups, alcohol groups, ether groups, aldehyde groups, ketonegroups, carboxylic acid groups, acyl groups (for example carboxylic acidderivatives such as esters and amides), amine groups, nitro groups, andthe like. For example, the 4-methylpent-1-yl radical is a C₆ aliphaticradical comprising a methyl group, the methyl group being a functionalgroup which is an alkyl group. Similarly, the 4-nitrobut-1-yl group is aC₄ aliphatic radical comprising a nitro group, the nitro group being afunctional group. An aliphatic radical may be a haloalkyl group whichcomprises one or more halogen atoms which may be the same or different.Halogen atoms include, for example; fluorine, chlorine, bromine, andiodine. Aliphatic radicals comprising one or more halogen atoms includethe alkyl halides trifluoromethyl, bromodifluoromethyl,chlorodifluoromethyl, hexafluoroisopropylidene, chloromethyl,difluorovinylidene, trichloromethyl, bromodichloromethyl, bromoethyl,2-bromotrimethylene (e.g., —CH₂CHBrCH₂—), and the like. Further examplesof aliphatic radicals include allyl, aminocarbonyl (i.e., —CONH₂),carbonyl, 2,2-dicyanoisopropylidene (i.e., —CH₂C(CN)₂CH₂—), methyl(i.e., —CH₃), methylene (i.e., —CH₂—), ethyl, ethylene, formyl (i.e.,—CHO), hexyl, hexamethylene, hydroxymethyl (i.e., —CH₂OH),mercaptomethyl (i.e., —CH₂SH), methylthio (i.e., —SCH₃),methylthiomethyl (i.e., —CH₂SCH₃), methoxy, methoxycarbonyl (i.e.,CH₃OCO—), nitromethyl (i.e., —CH₂NO₂), thiocarbonyl, trimethylsilyl(i.e., (CH₃)₃Si—), t-butyldimethylsilyl, 3-trimethyoxysilylpropyl (i.e.,(CH₃O)₃SiCH₂CH₂CH₂—), vinyl, vinylidene, and the like. By way of furtherexample, a C₁-C₁₀ aliphatic radical contains at least one, but no morethan 10, carbon atoms. A methyl group (i.e., CH₃—) is an example of a C₁aliphatic radical. A decyl group (i.e., CH₃(CH₂)₉—) is an example of aC₁₀ aliphatic radical.

As noted herein, in one embodiment, the present invention provides anamino-siloxane composition comprising structure I

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; R³ isindependently at each occurrence R¹ or R⁴, wherein R⁴ comprisesstructure II

and wherein R² is independently at each occurrence hydrogen or a C₁-C₁₀aliphatic radical; X is independently at each occurrence a NH₂ group ora cyano group; m is independently at each occurrence an integer from1-5; n is independently at each occurrence an integer from 0-5; and m isindependently at each occurrence an integer from 1-5; p is an integerfrom 0-100, and q is an integer from 0-500, with the proviso that atleast one of R³ is R⁴. In one embodiment, the amino-siloxane havingstructure I includes nitrogen in an amount of at least about 1.3%. Inanother embodiment, the amino-siloxane having structure I includesnitrogen in an amount of at least about 3.2%. In yet another embodiment,the amino-siloxane having structure I includes nitrogen in an amount ofat least about 6.4%. Amino-siloxane compositions having structure I areillustrated in Table 1 below.

TABLE 1 Examples of Amino-Siloxane Compositions Having Structure 1 EntryStructure R¹ R² n m X p q Ia

Me Et 1 1 NH₂ 0 0 Ib

Me Et 0 1 NH₂ 0 0 Ic

Me H 1 3 CN 0 0 Id

Me H 1 3 NH₂ 0 0 Ie

Me Me 1 1 NH₂ 1 0 If

Me Et 0 3 CN 0 0 Ig

Me Et 1 2 NH₂ 0 4 Ih

Me Et 1 2 NH₂ 0 0 Ij

Me H 1 3 NH₂ 0 0 Ik

Me H 1 3 NH₂ 1 0

In one embodiment, the amino-siloxane has structure Ia.

In another embodiment, the amino-siloxane has structure Ib.

In another embodiment, the amino-siloxane has structure Ic

In another embodiment, the amino-siloxane has structure Ie

In one embodiment, the present invention provides an amino-siloxanecomposition comprising structure III

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; X isindependently at each occurrence an NH₂ group or a cyano group; n isindependently at each occurrence an integer from 0-5, and m isindependently at each occurrence an integer from 1-5. Amino-siloxanecompositions having structure III are illustrated in Table 2 below.

TABLE 2 Examples of Amino-Siloxane Compositions Having Structure IIIEntry Structure R¹ m n X 2a

Me 1 0 CN 2b

Me 1 1 NH₂ 2c

Me 3 0 CN 2d

Et 2, 1 2 NH₂

In one embodiment, the amino-siloxane composition has structure IIIa.

In another embodiment, the amino-siloxane composition has structureIIIb.

In one embodiment, the present invention relates to amino-siloxanecarbon dioxide absorbents and methods of using the absorbents to absorbcarbon dioxide from process streams, e.g., as may be produced by methodsof generating electricity. Conventional carbon dioxide absorbents lackone or more of the properties considered important, if not critical, tocommercial feasibility of their use in many technologies. MEA-basedaqueous absorbents, for example, may not be suited for use with largevolumes of CO₂-containing exhaust gases. As a result, the use ofMEA-based absorbents under such circumstances may be prohibitivelyenergy intensive and costly for implementation.

In one embodiment, the present invention provides amino-siloxanes usefulas carbon dioxide absorbents which are liquids under ambient conditions,and which remain liquids following exposure to carbon dioxide. In oneembodiment, the present invention provides a liquid amino-siloxanehaving structure I, which reacts with carbon dioxide to form a reactionproduct referred to as an adduct of the amino-siloxane with carbondioxide, the adduct also being a liquid under ambient conditions. Inanother embodiment, the adduct may be a solid under ambient conditions.In another embodiment, the amino-siloxane composition having structureII reacts with carbon dioxide to form a reaction product or an adduct ofthe amino-siloxane with carbon dioxide, the adduct also being a liquidunder ambient conditions. In certain embodiments, the physical state ofthe adduct of the amino-siloxane composition with CO₂ can be controlledby limiting the degree to which the amino-siloxane composition has beenfully reacted with CO₂. For example, it may be possible and advantageousto limit the time and conditions of contacting the amino-siloxanecomposition with CO₂, such that the adduct contains less than thetheoretical amount of CO₂ derived structural units (i.e. carbamategroups). Those skilled in the art will appreciate that a primary orsecondary amine reacts with carbon dioxide to form an ammoniumcarbamate. In one embodiment, an amino-siloxane composition, which whenfully reacted with CO₂ is a solid under ambient conditions, can bemaintained in the liquid state when only partially reacted with CO₂. Inone embodiment, the present invention provides a reaction product of anamino-siloxane composition with CO₂, in which less than the theoreticalamount of CO₂ has reacted with the reactive groups of the amino-siloxanecomposition. In one embodiment, the degree of reaction with CO₂ is in arange from about 10 percent of theoretical to about 100 percent oftheoretical. In an alternate embodiment, the degree of reaction with CO₂is in a range from about 20 percent of theoretical to about 70 percentof theoretical. In yet another embodiment, the degree of reaction withCO₂ is in a range from about 30 percent of theoretical to about 50percent of theoretical.

The amino-siloxane composition undergoing the reaction with CO₂ to forma reaction product may be an essentially pure amino-siloxane, or may bea mixture of an amino-siloxane with one or more other components, forexample water or other diluents such as triethylene glycol. Typically,the amino-siloxane compositions are capable of absorbing an amount ofCO₂ corresponding to from about 1 to about 50 percent by weight of thecomposition. In one embodiment, the amino-siloxane compositions providedby the present invention and/or used according to the methods providedby the present invention, may be non-oligomeric and/or non-polymeric, inthat the materials do not contain “adjacent repeat units” derived frommonomeric units. As used herein, an adjacent repeat unit derived from amonomeric unit is a structural unit derived from a monomer and presentin a molecule chemically bound to an identical structural unit in thesame molecule without an intervening structure disposed between the two.Oligomeric materials are defined herein as molecules having between twoto twenty adjacent repeat units, and polymeric materials are definedherein as molecules having more than twenty adjacent repeat units.Notwithstanding the relatively low molecular weight of theamino-siloxane compositions provided by the present invention whencompared to analogous oligomeric and polymeric materials, theamino-siloxane compositions provided by the present invention typicallyexhibit a low vapor pressure. They usually also comprise functionalgroups (e.g. NH₂ groups, secondary amine groups) that either reactreversibly with, or have a high affinity for, CO₂. In anotherembodiment, the amino-siloxane compositions provided by the presentinvention and/or used according to the methods provided by the presentinvention, may be oligomeric and/or polymeric.

Amino-siloxane compositions provided by the present invention mayexhibit properties which are important for the reversible capture ofcarbon dioxide. Thus, amino-siloxane compositions provided by thepresent invention in various embodiments remain in a liquid state over arange of temperatures, are relatively non-volatile when compared to MEA,are thermally stable, and do not require a carrier fluid. Further, theamino-siloxane compositions provided by the present invention mayexhibit a high capacity for CO₂ absorption. The amino-siloxanecompositions provided by the present invention, owing to the presence ofsiloxane groups, are in various embodiments relatively hydrophobic,compared to MEA-based absorbents, and may be employed under nonaqueousconditions.

As noted, the amino-siloxane compositions provided by the presentinvention are relatively non-volatile liquids at room temperature, andmay be stable at high temperatures, e.g., up to about 150° C., andtypically may not require the use of additional solvents in order toachieve an acceptable viscosity level. As is amply disclosed in theExamples section of the present disclosure, the amino-siloxanecompositions comprising functional groups which are reversibly reactivewith carbon dioxide may be prepared efficiently and with a high level ofstructural diversity.

The amino-siloxane compositions provided by the present invention maydesirably be functionalized with groups that enhance the net capacity ofthe compositions for CO₂ absorption. Functional groups that are expectedto be CO₂-philic, and thus enhance the affinity of the amino-siloxanecomposition for CO₂, include acetate groups, carbonate groups, ketonegroups, quaternary ammonium groups, imine groups, guanidine groups, andamidine groups. Examples of amine functional groups that exhibitCO₂-reactivity include primary amine groups and secondary amine groups.Numerous methods for the introduction of such functional groups areknown to those of ordinary skill in the art using techniques such ashydrosilylation and displacement. Michael A. Brook's book, Silicon inOrganic, Organometallic, and Polymer Chemistry (Wiley VCH Press, 2000),provides useful guidance in this area, and is incorporated herein byreference in its entirety for purposes related to synthetic methods. Inone embodiment, the present invention provides amino-siloxanecompositions comprising one or more guanidine groups or amidine groups.A primary amine group (NH₂) may be transformed into a guanidine groupunder mild conditions by reaction with the Vilsmeier salt of, forexample, tetraisopropyl thiourea or diisopropyl carbodiimide, to providea guanidine group. Similarly, amidine groups may be prepared by, forexample, by reaction of a primary or secondary amine group with ethylacetimidate (the Pinner reaction product of acetonitrile with ethanol).

Optionally, the amino-siloxane composition provided by the presentinvention may also include other components, such as oxidationinhibitors to increase oxidative stability, and anti-foaming agents. Theuse of oxidation inhibitors, also called antioxidants, can be especiallyadvantageous in those embodiments of the invention wherein the aminegroups are sensitive to oxidation.

In one embodiment, the present invention provides a method of reducingthe amount of carbon dioxide in a process stream, comprising the step ofcontacting the stream with a carbon dioxide absorbent composition,comprising at least one amino-siloxane selected from the groupconsisting of amino-siloxanes having structure I, and amino-siloxaneshaving structure III

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; R³ isindependently at each occurrence R¹ or R⁴, wherein R⁴ comprisesstructure II

and wherein R² is independently at each occurrence hydrogen or a C₁-C₁₀aliphatic radical; X is independently at each occurrence an NH₂ group ora cyano group; m is independently at each occurrence an integer from1-5; n is independently at each occurrence an integer from 0-5; p is aninteger from 0-100, and q is an integer from 0-500; with the provisothat at least one of R³ is R⁴. In one embodiment, the present inventionprovides a reaction product of an amino-siloxane composition havingstructure I and/or II with carbon dioxide. The experimental section ofthis disclosure provides detailed guidance on the preparation of suchreaction products, also referred to at times herein as adducts of theamino-siloxane composition with carbon dioxide.

In another embodiment, the present invention provides a method ofreducing the amount of carbon dioxide in a process stream comprisingcontacting the stream with a carbon dioxide absorbent comprising atleast one amino-siloxane having structures I and/or III. The carbondioxide absorbents provided herein are expected to provide advantageswhen utilized to remove CO₂ from process gases, as compared to thosecurrently commercially available and/or utilized for this purpose. Assuch, a method of reducing the carbon dioxide in a process stream isprovided, and comprises contacting the process stream with the carbondioxide absorbents described herein. The process stream so treated maybe any wherein the level of CO₂ therein is desirably reduced, and inmany processes, CO₂ is desirably reduced at least in the exhaust streamsproduced thereby. The process stream is typically gaseous, but maycontain solid or liquid particulates, and may be at a wide range oftemperatures and pressures, depending on the application. In oneembodiment, the process stream may be a process stream from industries,such as chemical industries, cement industries, steel industries, fluegases from a power plant, and the like. In one embodiment, the processstream may be a fuel stream. In another embodiment, the fuel stream maybe a natural gas stream or a syngas stream. In yet another embodiment,the process stream is selected from the group consisting of a combustionprocess, a gasification process, a landfill, a furnace, a steamgenerator, a boiler and combinations thereof.

The carbon dioxide absorbents, and methods of using them, providedherein may benefit from economies of scale which lower their cost.Further, the absorbents have relatively low volatility, high thermalstability, and can be provided using the synthetic methods disclosedherein. It is believed that the compositions provided by the presentinvention will be especially useful in power plants requiring means forreducing carbon dioxide emissions. Thus, in one embodiment, the presentinvention provides a method for reducing carbon dioxide emissionsutilizing the compositions provided by the present invention.

EXAMPLES

The following examples illustrate methods and embodiments in accordancewith the invention. Unless specified otherwise, all ingredients may becommercially available from such common chemical suppliers as AlphaAesar, Inc. (Ward Hill, Mass.), Sigma Aldrich (St. Louis, Mo.), SpectrumChemical Mfg. Corp. (Gardena, Calif.), and the like.

Carbon dioxide uptake measurements were carried out using lab scaletechniques.

Representative Lab-Scale Example:

To a tared, 25 mL, 3-neck, round bottom flask equipped with a mechanicalstirrer, gas inlet tube and a gas bubbler was placed a pre-determinedweight of solvent (typically approximately 2 grams). The solvent wasstirred and heated in an oil bath at 40° C. while a constant flow of dryCO₂ was passed into the flask. After 2 hours of exposure to CO₂, the gaswas turned off, the reaction flask was weighed, and the weight recorded.The difference in weight was the amount of CO₂ that had been adsorbed,which can be expressed as a % weight gain from the original weight ofthe solvent.

Example 1 Preparation of Amino-Siloxane Composition (Ia)

A solution of 1,3-bis(2,2-dicyanobutyl)-1,1,3,3-tetramethyldisiloxane(2.45 g, 7.1 mmol) in diethylether (25 mL) was added slowly over aperiod of 15 min to a mechanically stirred, pre-cooled slurry of lithiumaluminum hydride (2.49 g, 65.7 mmol) in diethylether (275 mL) at atemperature of about 0° C. under N₂, in order to maintain thetemperature of the mixture below 5° C. The mixture was stirred for 6hours, followed by addition of water (10 mL), 1 M NaOH (40 mL) and water(50 mL), in the given order, with vigorous stirring. This was followedby the addition of diethylether (100 mL). The reaction mixture was thenextracted with additional portions of diethylether (4×100 mL). Thediethylether layers were combined, dried with Na₂SO₄, filtered andconcentrated to an oil. The aqueous layer was further extracted withCHCl₃ (3×30 mL), and treated, following the method described above. Thecrude products were combined; dissolved in diethylether, and acidifiedwith concentrated HCl. This was followed by isolation of the salt as awhite solid. The isolated solid was dissolved in water, neutralized with1N NaOH, extracted with CHCl₃, dried with Na₂SO₄, and concentrated togive 1.02 g (40%) of the reaction product 1a as a colorless liquid.

The following data (e.g., spectroscopic data) were obtained for theproduct 1a:

¹H NMR (CDCl₃) δ: 2.39 (s, 8H), 1.14 (q, J=7.6 Hz, 8H), 1.08 (br s, 8H),0.64 (t, J=7.6 Hz, 6H), 0.41 (s, 4H), −0.02 (s, 12H).

¹³C {¹H}NMR (CDCl₃): 48.1, 41.0, 27.2, 23.6, 7.8, 3.0 ppm. FT-IR (neat):3377, 3296, 2959, 2852, 1604, 1463, 1408, 1379, 1253, 1044, 836, 802,750 cm⁻¹.

The exact mass (MS:) calculated for C₁₆H₄₃N₄OSi₂ (M+H⁺) was 363.2975,observed (M+H⁺): 363.2949.

Example 2 Preparation of Amino-Siloxane Composition (Ib)

To a solution of 2-ethylmalononitrile (2.0 g, 21.2 mmol) intetrahydrofuran (THF, 10 mL) at 0° C. was added potassium t-butoxide(1.75 g, 15.6 mmol), to provide a clear brown solution. A solution of1,3-bis(iodomethyl)1,1,3,3-tetramethyldisiloxane (2.93 g, 14.2 mmol) inTHF (6 mL) was added drop-wise, using an addition funnel, when all thepotassium t-butoxide had dissolved. On completion of the addition of theabove solution, a fresh portion of THF (6 mL) was used to rinse theaddition funnel. The reaction mixture was then allowed to warm to roomtemperature. As the reaction preceded, the solution lightened in colorand solid-precipitated. At the end of three days, the reaction mixturewas filtered, and the solids were washed with THF. The solution wasconcentrated on a rotary evaporator and the residue thus obtained waspartitioned between chloroform and water. The organics combined and werewashed with water, dilute sodium hydrosulfite, followed by water, andfinally with saturated sodium chloride solution, followed by drying overanhydrous sodium sulfate. Following the wash, the solvent was removedunder reduced pressure, yielding 2.67 g of crude material as a yellowoil. Purification of the crude product was carried out using columnchromatography (200-400 mesh silica gel, 3.5:1 hexanes:ethyl acetate aseluent). The result was 1.48 g (60%) of reaction product 1b, obtained asa white solid. Further purification of the reaction product 1b wascarried out, employing recrystallization with a heptane:acetone solventmixture.

The following data (e.g., spectroscopic data) were obtained for theproduct 1b:

The melting point of the material was determined to be 39-41° C.

¹H NMR (CDCl₃) δ: 2.03 (q, J=8 Hz, 4H), 1.39 (s, 4H), 1.26 (t, J=8 Hz,6H), 0.35 (s, 12H).

¹³C {¹H}NMR (CDCl₃): 116.61, 35.33, 33.96, 27.03, 9.94, 1.44 ppm. FT-IR(neat): 2982, 2944, 2885, 2245, 1580, 1462, 1410, 1392, 1329, 1311,1256, 1239, 1116, 1082, 959, 935, 844, 809, 791 cm⁻¹.

The exact mass (MS): Calculated for C₁₆H₂₇N₄OSi₂ (M+H⁺): 333.2757;observed (M+H⁺): 333.2755.

Example 3 Preparation of Amino-Siloxane Composition (Ic)

To a solution of malononitrile (8.42 g, 127 mmols) in THF (35 mL) at 0°C., was added potassium t-butoxide (5.15 g, 45.9 mmols). The resultingmilky pink solution was stirred under nitrogen for 15 minutes, followedby dropwise addition of1,3-bis(3-iodopropyl)-1,1,3,3-tetramethyldisiloxane (10.0 g, 42.5 mmol)in THF (10 mL) over a period of 20 minutes, using an addition funnel.The addition funnel was rinsed using THF (5 mL). The reaction mixturewas allowed to warm to room temperature and allowed to stay overnight.At the end of the stipulated time, the THF was removed using a rotaryevaporator, and the residue was partitioned between chloroform and 10%HCl. The organics were then washed twice with deionized water and onceeach with dilute NaHSO₃, water, and saturated sodium chloride. Followingthe washing step, the organics were dried over anhydrous sodium sulfate,and the solvent was removed on a rotary evaporator to yield 7.2 g (98%)of the crude product as a red oil. Further purification of the crudeproduct was carried out using column chromatography (200-400 mesh silicagel, 3:1 hexanes:ethyl acetate as eluent), to yield the reaction product1c (6.26 g, 85% yield) as a light yellow oil.

The following data (e.g., spectroscopic data) were obtained for theproduct 1c:

1H NMR (CDCl3) δ: 3.78 (t, J=8 Hz, 2H), 2.04 (q, J=8 Hz, 4H), 1.63 (m,4H), 0.57 (m, 4H), 0.09 (s, 12H).

13C{1H} NMR (CDCl3): 113.02, 33.67, 22.27, 20.66, 17.05, 0.27 ppm.

FT-IR (neat): 2958, 2923, 2882, 2258, 1578, 1460, 1412, 1349, 1314,1260, 1180, 1066, 849, 798, 767, 706 cm−1.

The exact mass MS: calculated for C16H27N4OSi2 (M+H+): 347.1723,observed (M+H+): 347.1714.

Example 4 Preparation of Amino-Siloxane Composition (2a)

Preparation of 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane:1,3-Bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane (20.0 g, 173 mmolsalkyl chloride) was combined with acetone (80 mL) and sodium iodide(39.0 g, 260 mmol). The reaction mixture was then heated to atemperature of about 35-40° C. overnight. At the end of the stipulatedtime the reaction mixture was cooled and filtered to remove any salts.The acetone was then removed using a rotary evaporator. The residueobtained, which was a mixture of solid and liquid, was then partitionedbetween heptane and water. The organic layer was washed with dilutesodium hydrosulfite, water, and saturated sodium chloride, and driedover anhydrous sodium sulfate. The solvent was removed on a rotaryevaporator to yield the product compound1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane (30.3 g, 85%) as acolorless oil.

The following data (e.g., spectroscopic data) were obtained for productcompound 1,3-bis(iodomethyl)-1,1,3,3-tetramethyldisiloxane:

¹H NMR (CDCl₃) δ: 2.01 (s, 4H), 0.28 (s, 12H).

¹³C {¹H}NMR (CDCl₃): −0.29, −12.49.

Malononitrile (6.4 g, 97 mmol) in THF (35 mL) was cooled in an ice bathunder nitrogen, followed by addition of solid potassium t-butoxide (5.4g, 48 mmol), to yield a milky pink reaction mixture. After approximately15 minutes, a solution of1,3-bis(iodomethyl)1,1,3,3-tetramethyldisiloxane (10.0 g, 48 mmols alkyliodide) in THF (10 mL) was added dropwise over a period of 10 minutesusing an addition funnel. The addition funnel was then rinsed with THF(5 mL). The ice bath was removed and the reaction mixture was allowed towarm to room temperature and kept overnight. The reaction mixture turnedfrom pink to orange. At this point, the reaction mixture was filtered toremove solids, and the solvent was removed under reduced pressure. Theresidue was dissolved in chloroform and washed with 5% NaOH, followed bydeionized water (4×), and dried over anhydrous sodium sulfate. Thesolution was then filtered, and solvent was removed using a rotaryevaporator. The crude solid product was then recrystallized twice from amixture of cyclohexane and isopropanol (20 mL/2 mL to provide thereaction product 2a (3.6 g, 67% yield) as a white solid.

The following data (e.g., spectroscopic data) were obtained for theproduct 2a:

The melting point was determined to be 132-134° C.

¹H NMR (CDCl₃) δ: 1.46 (s, 4H) 0.32 (s, 12H).

¹³C {¹H}NMR (CDCl₃): 118.08, 28.77, 26.42, 1.47.

FT-IR (neat): 2966, 2240, 1425, 1252, 1023, 1001, 968, 817, 762, 695Cm⁻¹.

The exact mass MS: calculated for: C₉H₁₇N₂OSi₂ (M+H⁺): 225.0879;observed (M+H⁺): 225.0870.

Example 5 Preparation of Amino-Siloxane Compound (2b)

A solution of 2,2,6,6-tetramethyl-1,2,6-oxadisilinane-4,4-dicarbonitrile(3.4 g, 15.1 mmol) in THF/diethylether (20 mL/20 mL) was added slowlyover a period of 25 min to a mechanically stirred, pre-cooled slurry oflithium aluminum hydride (2.7 g, 70 mmol) in diethylether at −5° C.under N₂. The temperature of the reaction mixture was maintained below5° C. The reaction mixture was stirred for 2.5 h, followed by theaddition of water (10 mL), 20% NaOH (20 mL), and additional water (40mL) (in that sequence), with vigorous stirring. An additional amount ofdiethylether was added (50 mL), to form a two phase slurry. Thediethylether was decanted from the 2-phase slurry, and a white sludgewas extracted with {additional} diethylether (2×50 mL). The diethyletherlayers were combined, dried with MgSO₄, filtered, and concentrated toobtain a hazy white liquid which was fractionally distilled at 75-77°C./0.2 torr, to give 2.1 g (60%) reaction product 2b, as a colorlessliquid.

The following data (e.g., spectroscopic data) were obtained for theproduct 2b:

¹H NMR (CDCl₃) δ: 2.70 (s, 4H); 1.93 (br s, 4H); 0.58 (s, 4H); 0.15 (s,12H).

¹³C {¹H} NMR (CDCl₃): 54.2, 40.7, 22.7, 2.7 ppm.

FT-IR (neat): 3385, 3305, 2961, 2899, 2869, 1603, 1460, 1417, 1314,1259, 1189, 1058, 988, 853, 816, 761, 644, 601 cm⁻¹.

The exact mass MS: calculated for: C₉H₂₅N₂OSi₂ (M+H⁺): 233.1505;observed (M+H⁺): 233.1495.

Example 6 Preparation of Cyanosiloxane 1f

To an ice cold solution of 2-ethylmalononitrile (4.5 g, 47.8 mmol) inTHF (25 mL) was added potassium t-butoxide (4.3 g, 38.3 mmol). Thiscaused the mixture to turn clear brown. Once all of the KOtBu haddissolved (10-15 minutes), a solution of1,3-bis(iodopropyl)1,1,3,3-tetramethyldisiloxane (7.48 g, 31.8 mmol RI)in THF (8 mL) was added dropwise. On completion of the addition, theaddition funnel was rinsed with another portion of fresh THF (3 mL). Thereaction mixture was allowed to warm to room temperature for 2 hours. Asthe reaction proceeded, the color changed from clear brown to milkyyellow. At the end of the stipulated time, the reaction mixture wasfiltered and the solids were washed with THF. The THF solution thatresulted was then stripped under reduced pressure. The residue was thenpartitioned between chloroform and water. The organic phase was washedwith water (two portions), followed by washing with dilute sodiumhydrosulfite, and finally with saturated sodium chloride solution. Theorganic phase was dried over anhydrous potassium carbonate, and thechloroform was stripped off under reduced pressure. The crude product 1fobtained was purified using column chromatography (200-400 mesh silicagel, 3:1 heptane:ethyl acetate as eluent). The product 1f was obtainedas a slightly yellow oil (5.38 g ˜84%).

The following data (e.g., spectroscopic data) were obtained for theproduct 1f:

¹H NMR (CDCl₃) δ: 1.98 (q, J=8 Hz, 4H, CH ₂CH₃), 1.93 (m, 4H,CH₂—C(CN)₂), 1.69 (m, 4H, CH₂CH ₂CH₂), 1.26 (t, J=8 Hz, 6H, CH₂CH ₃),0.61 (m, 4H, CH₂Si), 0.10 (s, 12H, CH₃—Si).

¹³C {¹H}NMR (CDCl₃): 115.67, 40.54, 38.67, 31.59, 19.82, 17.74, 9.88,0.34. FT-IR: 2979, 2957, 2884, 2247, 1461, 1412, 1303, 1255, 1193, 1063,843, 801, 765 cm⁻¹.

Exact mass MS: Calc'd for: C₂₀H₃₅N₄OSi₂ (M+H⁺); 403.2349. Found;403.2362.

Example 7 Preparation of Aminosiloxane 1h

To an ice cold mixture of lithium aluminum hydride (1.80 g, 47.4 mmols,190 mmols H) in ether (100 mL) was added dropwise, under nitrogen, asolution of 1,3-bis(4,4-dicyanohexyl)-1,1,3,3-tetramethyldisiloxane 1f(3.16 g, 7.8 mmols, 31.4 mmols CN) in ether (50 mL). The reactionmixture was allowed to slowly warm to room temperature where it was keptfor three hours. At the end of the stipulated time the reaction mixturewas cooled back down to about 0° C., followed by addition of 10 mL ofwater over approximately 15 minutes and 50% sodium hydroxide 0.5 mL. Thereaction mixture warmed to room temperature, and was filtered to removesalts and dried over anhydrous potassium carbonate. The solution wasstripped under reduced pressure to yield the product 1h as a slightlyyellow oil. (2.92 g, ˜89%).

The following data (e.g., spectroscopic data) were obtained for theproduct 1h:

¹H NMR (CDCl₃) δ: 2.51 (s, 8H, CH ₂NH₂), 1.22 (q, J=8 Hz, 4H, CH ₂CH₃),1.17-1.20 (m, 8H, CH₂s), 1.00 (br s, 8H, NH₂), 0.79 (t, J=8 Hz, 6H,CH₂CH ₃), 0.49 (m, 4H, CH₂Si), 0.03 (s, 12H, CH₃—Si)

¹³C {¹H}NMR (CDCl₃): 45.65, 40.61, 36.23, 24.53, 19.42, 16.58, 7.42,0.46. FT-IR: 3377, 3298, 2957, 2926, 2865, 1606, 1462, 1252, 1062, 840,802, 723 cm⁻¹.

Exact mass MS: Calc'd for: C₂₀H₅₁N₄OSi₂ (M+H⁺); 419.3601. Found;419.3596.

Example 8 Preparation of Aminosiloxane Oligomer 1g

Aminosiloxane 1h (2.5 g, 5.97 mmol) was combined withoctamethylcyclotetrasiloxane (1.77 g, 5.97 mmols of dimethylsiloxygroups) and 40 mg of tetramethylammonium hydroxide pentahydrate. Thereaction mixture was heated to 85° C. to 90° C. under house vacuum. Thevacuum was broken with nitrogen when the required temperature wasreached. The reaction mixture was allowed to stir for about 5 hours,following which the temperature was increased to decompose the catalyst.When the temperature reached approximately 130° C., a moderate vacuumwas applied. Heating was continued up to a temperature of 165° C., andthe volatile catalyst decomposition by-products were distilled off. Atthis point, the reaction mixture was cooled to room temperature andfiltered through a small amount of Celite 545 to remove some haziness.The product 1g was obtained as a light yellow oil (3.86 g, 90%).

The following data (e.g., spectroscopic data) were obtained for theproduct 1g:

¹H NMR (CDCl₃) δ: 2.50 (s, 8H, CH ₂NH₂), 1.14-1.26 (m, 12H, CH₂s), 0.93(br s, 8H, NH₂), 0.78 (t, J=8 Hz, 6H, CH₂CH ₃), 0.50 (m, 4H, CH₂Si),0.0-0.08 (series of singlets, 38H, CH₃—Si).

Example 9 Reaction of Amino-Siloxane Ia with Carbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet, and heated with atemperature controlled oil bath, was charged 0.5825 g of1,3-bis(2,2-bis(aminomethyl)butyl)-1,1,3,3-tetramethyldisiloxane Ia. DryCO₂ gas was introduced at a rate of ˜50 mL/min into the flask, via aglass tube positioned approximately 10 mm above the surface of thestirred liquid. Contacting with CO₂ was continued for 2 hours at 40° C.,after which time the exterior of the flask was cleaned and the flaskweighed. The total weight gain of 0.0280 g corresponded to 19.8% of thetheoretical amount of weight that should have been gained if all theamine groups had reacted with CO₂ (i.e. if the degree of reaction hadbeen 100%). The reaction product was also a solid, and constitutes thereaction product of amino-siloxane Ia with carbon dioxide.

Example 10 Reaction of Triethylene Glycol and Amino-Siloxane Ia withCarbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet, and heated with atemperature controlled oil bath, was charged 0.5768 g of1,3-bis(2,2-bis(aminomethyl)butyl)-1,1,3,3-tetramethyldisiloxane Ia and0.5946 g of triethylene glycol (TEG). Dry CO₂ gas was introduced at arate of ˜50 mL/min into the flask, via a glass tube positionedapproximately 10 mm above the surface of the stirred liquid. Contactingwith CO₂ was continued for 2 hours at 40° C., after which time theexterior of the flask was cleaned, and the flask weighed. The totalweight gain of 0.0831 g corresponded to 59.4% of the theoretical amountof weight that should have been gained if all the amine groups hadreacted with CO₂ (i.e. if the degree of reaction had been 100%). Thereaction product was a viscous liquid, and constitutes the reactionproduct of amino-siloxane Ia with carbon dioxide.

Example 11 Reaction of Amino-Siloxane 2b with Carbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet, and heated with atemperature controlled oil bath, was charged 0.8380 g of2,2,6,6-tetramethyl-1,2,6-oxadisilinane-4-4-diyl)dimethanamine. Dry CO₂gas was introduced at a rate of ˜50 mL/min into the flask via a glasstube positioned approximately 10 mm above the surface of the stirredliquid. Contacting with CO₂ was continued for 2 hours at 40° C., afterwhich time the exterior of the flask was cleaned and the flask weighed.The total weight gain of 0.1374 g corresponded to 86.5% of thetheoretical amount of weight that should have been gained if all theamine groups had reacted with CO₂ (i.e. if the degree of reaction hadbeen 100%). The reaction product was also a solid and constitutes thereaction product of amino-siloxane 2b with carbon dioxide.

Example 12 Reaction of TEG and Amino-Siloxane 2b with Carbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet, and heated with atemperature controlled oil bath, was charged 0.7822 g of2,2,6,6-tetramethyl-1,2,6-oxadisilinane-4-4-diyl)dimethanamine 2b and0.8059 g of triethylene glycol (TEG). Dry CO₂ gas was introduced at arate of ˜50 mL/min into the flask via a glass tube positionedapproximately 10 mm above the surface of the stirred liquid. Contactingwith CO₂ was continued for 2 hours at 40° C., after which time theexterior of the flask was cleaned and the flask weighed. The totalweight gain of 0.0892 g corresponded to 60.2% of the theoretical amountof weight that should have been gained if all the amine groups hadreacted with CO₂ (i.e. if the degree of reaction had been 100%). Thereaction product was a viscous liquid and constitutes the reactionproduct of amino-siloxane 2b with carbon dioxide.

Example 13 Reaction of Amino-Siloxane 1h with Carbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet and heated with atemperature controlled oil bath, was charged 1.4949 g of aminosiloxane1h. Dry CO₂ gas was introduced at a rate of ˜50 mL/min into the flaskvia a glass tube positioned approximately 10 mm above the surface of thestirred liquid. Contacting with CO₂ was continued for 2 hours at 40° C.,after which time the exterior of the flask was cleaned and the flaskweighed. The total weight gain of 0.2003 g corresponded to 64% of thetheoretical amount of weight that should have been gained if all theamine groups had reacted with CO₂ (i.e. if the degree of reaction hadbeen 100%). The reaction product was a powdery solid, and constitutesthe reaction product of amino-siloxane 1h with carbon dioxide.

Example 14 Reaction of Amino-Siloxane 1h with Carbon Dioxide inTriethylene Glycol

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet and heated with atemperature controlled oil bath, was charged 0.8060 g of aminosiloxane1h and 0.8196 g TEG. Dry CO₂ gas was introduced at a rate of ˜50 mL/mininto the flask via a glass tube positioned approximately 10 mm above thesurface of the stirred liquid. Contacting with CO₂ was continued for 2hours at 40° C., after which time the exterior of the flask was cleanedand the flask weighed. The total weight gain of 0.1615 g corresponded to95% of the theoretical amount of weight that should have been gained ifall the amine groups had reacted with CO₂ (i.e. if the degree ofreaction had been 100%). The reaction product was a soft waxy materialand constitutes the reaction product of amino-siloxane 1h with carbondioxide.

Reaction of Amino-Siloxane Oligomer 1g with Carbon Dioxide

To a tared, 25 mL, three-neck, round-bottom flask equipped with amechanical stirrer, gas inlet and a gas outlet and heated with atemperature controlled oil bath, was charged 2.0208 g of aminosiloxaneoligomer 1g. Dry CO₂ gas was introduced at a rate of ˜50 mL/min into theflask via a glass tube positioned approximately 10 mm above the surfaceof the stirred liquid. Contacting with CO₂ was continued for 2 hours at40° C., after which time the exterior of the flask was cleaned, and theflask weighed. The total weight gain of 0.2047 g corresponded to 82% ofthe theoretical amount of weight that should have been gained if all theamine groups had reacted with CO₂ (i.e. if the degree of reaction hadbeen 100%). The reaction product was a powdery solid and constitutes thereaction product of amino-siloxane oligomer 1g with carbon dioxide.

This written description uses examples to disclose some embodiments ofthe invention, including the best mode, and also to enable any personskilled in the art to practice the invention, including making and usingany devices or systems and performing any incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

What is claimed is:
 1. A method of reducing the amount of carbon dioxidein a process stream, comprising the step of contacting the stream with acarbon dioxide absorbent comprising at least one amino-siloxane compoundselected from the group consisting of amino-siloxanes having structure Iand amino-siloxanes having structure III,

wherein R¹ is independently at each occurrence C₁-C₅ alkyl; R³ isindependently at each occurrence R¹ or R⁴, wherein R⁴ comprisesstructure II

and wherein R² is independently at each occurrence hydrogen or a C₁-C₁₀aliphatic radical; X is independently at each occurrence a NH₂ group ora cyano group; m is independently at each occurrence an integer from1-5; n is independently at each occurrence an integer from 0-5; p is aninteger from 0-100; and q is an integer from 0-500; with the provisothat at least one of R³ is R⁴.
 2. The method according to claim 1,wherein the amino-siloxane is a liquid.
 3. The method according to claim1, wherein said process stream is at least one selected from the groupconsisting of a combustion process, a gasification process, a landfill,a furnace, a steam generator, and a boiler.
 4. The method according toclaim 1, wherein said process stream is a fuel stream.
 5. The methodaccording to claim 4, wherein said fuel stream comprises natural gas. 6.The method according to claim 4, wherein said fuel stream comprises syngas.